The following disclosure is related to systems and methods for applying neural stimulation to and/or receiving neural signals from a patient, for example, at a surface site on or proximate to the patient's cortex.
A wide variety of mental and physical processes are controlled or influenced by neural activity in particular regions of the brain. The neural functions in some areas of the brain (e.g., the sensory or motor cortices) are organized according to physical or cognitive functions. Several other areas of the brain also appear to have distinct functions in most individuals. In the majority of people, for example, the occipital lobes relate to vision, the left interior frontal lobes relate to language, and the cerebral cortex appears to be involved with conscious awareness, memory, and intellect.
Many problems or abnormalities can be caused by damage, disease, and/or disorders of the brain. Effectively treating such abnormalities may be very difficult. For example, a stroke is a common condition that damages the brain. Strokes are generally caused by emboli (i.e., obstruction of a blood vessel), hemorrhages (i.e., rupture of a blood vessel), or thrombi (i.e., clotting) in the vascular system of a specific region of the brain. Such events generally result in a loss or impairment of neural function (e.g., neural functions related to facial muscles, limbs, speech, etc.). Stroke patients are typically treated using physical therapy that attempts to rehabilitate the loss of function of a limb or another affected body part. Stroke patients may also be treated using physical therapy plus an adjunctive therapy such as amphetamine treatment.
As another example, Parkinson's Disease (PD) is related to the degeneration or death of dopamine producing neurons in the substantia nigra region of the basal ganglia in the brain. As the neurons in the substantia nigra deteriorate, the reduction in dopamine causes abnormal neural activity that results in a chronic, progressive deterioration of motor function control and possibly other symptoms.
Neural activity in the brain can be influenced by electrical energy supplied from an external source such as a waveform generator. Various neural functions can be promoted or disrupted by applying an electrical current to the cortex or other region of the brain. As a result, researchers have attempted to use electrical or magnetic stimulation signals to control or affect brain functions. Electrical stimulation signals may comprise a series of electrical pulses that can affect neurons within a target neural population. Stimulation signals may be defined or described in accordance with stimulation signal parameters that include pulse amplitude, pulse frequency, stimulation signal duration, and/or other parameters.
In certain applications, such as deep brain stimulation, electrical stimulation is provided by a pulse system coupled to a plurality of therapy electrodes or electrical contacts. The pulse system is typically implanted into a patient at a subclavicular location, and the therapy electrodes can be implanted into the patient at a target site for stimulating the desired neurons.
FIG. 1 is a perspective view of an implantable electrode assembly 10 configured in accordance with the prior art. The electrode assembly 10 can be a Resume II electrode assembly provided by Medtronic, Inc., of 710 Medtronic Parkway, Minneapolis, Minn. 55432-5604. The electrode assembly 10 includes a plurality of plate electrodes 14a–d carried by a flexible substrate 12. A polyester mesh 11 is molded into the substrate 12 to increase the tensile strength of the substrate 12. A cable 16 houses four individually insulated leads 18a–d that extend into the substrate 12. A connector 20 joins with the receptacle 22 to form a coupling between the electrode assembly 10 and a power source (not shown).
One problem of using an electrode assembly 10 of the type shown in FIG. 1 is acquiring an appropriate placement at or upon a stimulation site. Certain obstacles may hinder an appropriate placement of conventional electrodes. In the case of stimulation in or upon the brain, the brain's anatomical structure may naturally render electrode placement upon the brain's surface a complicated undertaking. The brain is replete with convolutions and crevices, which may impede electrode placement at specific locations.
Furthermore, in some instances, brain damage or degeneration may cause an infarct or tissue atrophy, which may alter neural topography in the damaged region or area. Physically damaged tissue in a given region may alter neural topography in surrounding regions, further causing impediments to electrode placement. Thus, the presence of brain damage or degeneration may complicate electrode placement relative to obtaining an intended therapeutic outcome.
Another problem associated with using a conventional electrode 10 is that in certain situations, the electrode's structure itself may limit manners in which neural stimulation can be applied or delivered to a target neural population. In particular, an electrode 10 having a structure of the type shown in FIG. 1A may be significantly limited with respect to an extent to which an electric field distribution can be configured relative to a given target neural population. This may result in decreased neural stimulation efficacy, and/or other problems such as insufficient surface-to-contact coupling, unpredictable impedance, current leakages, unregulated stimulation parameters, elevated power consumption and shorter battery life. Moreover, placement of the therapy electrodes on an appropriate anatomical location for effectuating desired therapeutic results may be difficult and time consuming. There is a significant need to improve procedures for appropriately placing electrode devices at a desired treatment site.